The report finds that if the federal government and states act aggressively and the U.S. Environmental Protection Agency (EPA) retains its authority to regulate emissions, the U.S. may achieve a 14 percent cut in CO2 emissions by 2020 from 2005 levels. Longer term reductions remain uncertain, particularly without climate legislation.

However, if the federal government and state actions are “lackluster,” the 2020 reduction in CO2 emissions could be as little as 6 percent, according to the report.

The analysis finds that if the federal government and states move aggressively through 2016, federal agencies, primarily the U.S. EPA and the Departments of Transportation and Energy could use existing authorities to put the country on track to meet the Obama Administration’s reduction target.

After 2016, estimated reductions fall short of the Administration’s target, which WRI’s report suggests the need for additional tools, such as a carbon price, to reduce emissions.

“Without federal climate legislation that locks in longer-term economy-wide reductions, the longer-term picture is unclear,” says Nicholas Bianco, a senior associate at WRI and a co-author of the study.

The latest reports indicate that Senate Democrats won’t include carbon dioxide cuts in energy legislation, while Congress continues to try to block EPA’s carbon regulations and delay the EPA’s CO2 regulations for power plants and factories.

The report finds that the most useful federal regulatory tools to achieve reductions are the mobile source and New Source Performance Standard provisions of the Clean Air, Title VI of the Act to reduce hydrofluorocarbons, and the Department of Transportation’s vehicle fuel efficiency authority.